In a typical prior art application, a Newtonian reflector telescope includes a tube having an open outer end and a closed inner end. A concave primary mirror is carried against or near the closed inner end, and reflects a cone-shaped light pattern back toward the open end. A secondary mirror is supported within the tube near the open end, and is oriented at a 45 degree angle. The secondary mirror reflects the light generally perpendicular to the tube, and into an eyepiece carried on the outside of the tube. A typical eyepiece has a rack-and-pinion adjustment, and resembles a microscope.
The primary mirror has a focal length, i.e. a length between the primary mirror and the point or plane of focus, e.g. at the eyepiece. The focal ratio is the focal length divided by the diameter of the primary mirror.
A number of problems are associated with such reflector telescopes. A first problem is of a commercial nature, in that the tube and primary mirror of a first manufacturer are often incompatible with the focuser and eyepiece of a second manufacturer. Given a tube and primary mirror having a particular focal length and focal ratio, an eyepiece and associated focusing device (or camera or similar optical device) must be selected which is adapted for bringing into focus a fixed range of distances; e.g. 1000' to infinity. It is a characteristic of the market place that where the tube and primary mirror is made by a given manufacturer, the recommended eyepiece and associated focusing device will be so adapted. However, where a second manufacturer's devices (eyepiece, camera, etc.) are used with the tube and primary mirror of a first manufacturer, it is often the case that the device is unusable, due to incompatibility with focal characteristics of the primary mirror. As a result, it is often the case that a tube and primary mirror made by a first manufacturer must be fitted with a focuser and eyepiece made by that manufacturer. In this manner, many manufacturers tend to prevent the use of other manufacturers' equipment with their equipment.
A second problem results from the use of reflector telescopes. Depending on the focusing conditions, a focuser tube may extend from the eyepiece into the main tube of the telescope to an excessive degree. This results in occlusion of the view, in that some light entering the main tube is prevented from contacting the primary mirror because it is blocked by the focusing tube. With known reflector telescopes, this condition will result when the eyepiece is focused to one extreme.
A third problem results from the use of reflector telescopes. Since most reflector telescopes are designed for astronomical use, they are only able to focus at the most distant terrestrial objects. The reason for this inadequacy is that, given the focal length, the eyepiece and associated focuser are constructed for focusing at astronomically distant objects. Nevertheless, reflector telescopes are not inherently unable to be used for viewing extremely close objects. However, in the prior art, no successful strategy for focusing a single telescope from as little as 10 feet to infinite distance has been developed.
For the foregoing reasons, there is a need for a reflector telescope that will allow operation of any given telescope tube assembly and primary mirror with any given focuser and eyepiece assembly. The reflector telescope must operate with the focuser tube substantially out of the main telescope tube, while still allowing the eyepiece to be focused. Additionally, the reflector telescope should be adapted for sharp focus over a substantially greater range of distance than conventional reflector telescopes, and in particular should be adapted for focus on extremely close objects.